In recent years, lighting devices and luminaires adapted for solid-state light emitting devices as a light source, instead of an incandescent lamp or a fluorescent lamp, have been rapidly widespread. Examples of the solid-state light emitting devices include a light emitting diode and an organic electroluminescence (EL) device. For example, JP2011-108671A (hereinafter, referred to as Document 1) discloses a lighting device (an LED dimming device) which is adapted for light emitting diodes (LEDs) as a light source and is configured to control (to dim) the light intensity of the LEDs in accordance with a dimming signal supplied from a dimming level designator.
Incidentally, examples of schemes for dimming LEDs include: a dimming scheme by which LEDs are continuously supplied with a current and magnitude of the supplied current is changed (hereinafter, referred to as “a DC dimming scheme”); and a scheme by which a current supply to LEDs is periodically switched on and off and a ratio of a current supply period (on-duty ratio) is changed (hereinafter, referred to as “a burst dimming scheme”). The examples also includes a scheme which performs the DC dimming scheme when the dimming level is comparatively high (bright) and performs the burst dimming scheme when the dimming level is comparatively low (dark), as the conventional example described in Document 1.
Incidentally, a switching regulator is typically employed as a lighting circuit for lighting the LEDs. In the burst dimming scheme, the current supply period in which the switching regulator performs a switching operation thereof decreases in accordance with decrease in the dimming level. Thus, decrease in the dimming level will increase fluctuation in the number of switching operation performed by the switching regulator in current supply periods. Therefore, there is a problem in that the fluctuation of the light intensity increases in accordance with the decrease in the dimming level.